Studies have shown that vision impairment can have serious adverse effects on orientation/mobility (O/M). The long-term goal of this research program is to understand how vision impairment cause functional limitation in O/M. Research over the past several years has cataloged the effects of vision impairments on mobility and has identified the visual function measures that are predictive of mobility performance and effort. However, an understanding of how vision impairments affect the mechanisms underlying mobility is lacking. The visual control of mobility is complex, involving the processing of visual information such as the visual motion patterns generated by a moving (optic flow), as well as the planning, execution, and integration of eye, head, and body movements. The overall aim of the proposed research is to understand the contributions of perception of heading direction and scanning eye/head movements to mobility performance and effort. The perception of heading will be investigated by measuring by discrimination thresholds for the direction of heading with computer-generated optic flow patterns. Scanning eye and head movement patterns will be monitored and characterized as subjects perform the heading discrimination task as they navigate a mobility course. Mobility performance will be evaluated by measures of walking speed and number of unwanted contact, and the mental effort required for mobility will be evaluated by secondary task performance and self-perceived mobility. Subjects will include visually impaired persons with age related macular degeneration, retinitis pigmentosa, or glaucoma and normally sighted persons with and without simulated vision loss. In addition to addressing the basic science questions abut the role of eye movements in simulated and natural mobility and the relationship of perception of heading direction and mobility performance and effort, the proposed research will provide information that can have an immediate and direct impact on the development of mobility devices and vision rehabilitation regimens, e.g., effective visual training strategies, for people with vision impairment.